Fluoropolymers represent a class of compounds with noteworthy properties for a large number of applications, from paint or special coatings to sealing joints, via optics, microelectronics, energy such as photovoltaics, fuel cells and Li-Ion batteries, and membrane technology. Among these fluoropolymers, poly(vinylidene fluoride) (PVDF) is a polymer acknowledged for its chemical and heat stability. This polymer is prepared by radical polymerization from vinylidene fluoride (VDF). This fluorinated monomer is difficult to copolymerize with non-fluorinated monomers such as vinyl ethers, acrylates, methacrylates or styrenes. In order to improve certain properties of PVDF, such as adhesion, anti-corrosion of coatings, hydrophobicity or hydrophilicity, while at the same time retaining its properties, in particular of chemical and heat resistance, it is necessary to functionalize it by incorporating monomers bearing chemical functions. However, few functionalized PVDFs are known, because of the low number of functionalized or functionalizable monomers capable of satisfactorily copolymerizing with VDF.
Another known fluoropolymer, poly(trifluoroethylene), shares the same difficulties in terms of being functionalized, since trifluoroethylene (TrFE) is itself difficult to copolymerize with functional monomers such as vinyl ethers, acrylates, methacrylates and styrenes for example.
There is therefore a need to develop new fluorinated copolymers, in particular copolymers based on VDF and/or TrFE, which exhibit functionalities that make them suitable for applications that are more varied than those which are known, while at the same time keeping the specific properties provided by the fluorinated monomer.
Chlorotrifluoroethylene (CTFE) copolymerizes easily with other fluorinated monomers such as VDF or TrFE, but also with non-fluorinated monomers, in particular with vinyl ethers. The publication by Boschet F. and Améduri B. in Chem Rev, 2014, 114, 927-980 describes in detail the various known CTFE-based copolymers, which are classified in two categories: i) copolymers having a low proportion of comonomer, their properties being close to those of poly(chlorotrifluoroethylene) with regard to the thermoplastic nature and the high degree of crystallinity; and ii) copolymers containing electron-donor comonomers, said copolymers being obtained by a polymerization reaction of acceptor-donor type giving predominantly alternating structures. Among the latter category are alternating copolymers of formula poly(CTFE-alt-vinyl ethers), which are prepared by radical polymerization. At the current time, many alternating copolymers of this type have been prepared, in which said vinyl ether (VE) is an alkyl vinyl ether of formula CH2═CH—O—R in which R can be for example chosen from the following groups: alkyl, such as ethyl, butyl, isobutyl, 4-hydroxybutyl, 2-chloroethyl, 2-ethylhexyl, 2-hydroxyethyl, glycidyl, 3-chloro-(2,2-dimethylpropyl). Said vinyl ether can also be further functionalized with for example imidazole, carbonate or phosphonate groups in a step subsequent to the polymerization. In the abovementioned alternating copolymers, the CTFE:VE molar ratio is close to 1.
The present invention proposes providing novel functionalized fluorinated copolymers, in particular copolymers of VDF and/or TrFE functionalized by the regular incorporation into the polymer chain of triads (X-E-X) where X is a fluorinated monomer having at least one double bond which has an electron acceptor nature, that is to say which is electron-depleted, X being, on the one hand, copolymerizable with a fluorinated monomer such as VDF or TrFE, and, on the other hand, copolymerizable with a monomer E having at least one double bond which has an electron donor nature, that is to say which is electron-enriched, and comprising a functional or functionalizable group. Said triad is for example formed from chlorotrifluoroethylene (monomer X) and vinyl ethers (monomer E): (CTFE-VE-CTFE).